Heat-resisting glass



- tively rapid changes in temperature.

' Apr. 5, 1927.

" UNITED STATES- PATENT OFFICE."

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8 0 Drawing.

' My invention relates to the production of a stable, translucent, heat resisting glass of the boro-silicate type suitable for use 1n oven ware, laboratory vessels, or other utensils or articles which in use must be capable of withstanding high temperatures or reg;-

out fracture.

Glass of this character has usually contained silica 65% to 85% Shy weight), bor1c oxide 10% :to alkai oxides such as sodium and potassium 5% to 10%, and also small amounts of aluminum, calcium and magnesium oxides.

Heretofore the efforts to produce a satis-.'

factory glass for oven ware or other utensils or articles subject to high temperature have proceeded on the theory that the requisite thermal endurance must be obtained by reducing the coeflicient of expansion to a minimum. Fracture of glass sub- 'ected tora id heating or cooling occurs ecause of t e inequality in change of temperature as between one part of the body and the other, for example, as between the surface ofthe body and the interior portions thereof, this unequal change in temperature setting up internal strains that the body by minimizing thedifference in expansion may be incapable of withstanding. By re ducing the expansivity of the glass, that 1s,

between the highly heated and the less heated portions of theglass body the liability to fracture is, obviously diminished.

I have discovered, however, that a stable glass (stability referring to relative nonsolubility in water) of the. boro-silicate type can be obtained by increasing the toughness ofthe glass (non-brittleness) as well as by decreasing its coefficient of expansion and, in fact, that it is possible, by.

the novel method to be hereinafter described, to produce a very serviceable oven glass, for-example, in which the coefiicient' of expansion is, relatively speaking, 'high, .by a composition of the batch and manipulation of the melt which will increase the toughness of the glass sufficiently to compensate for the higher expansivity. I have dis covered further that the increased toughness is to be obtained by roducing in the melting operation a colloi al suspension of Application filed Hay 9, 1928. Serial 110.3,808.

certain ingredients and arresting the heating operation before the suspended particles are fully dissolved, as will occur inmost cases, at least, if the application of This colloidal condition manifests itself in the finished glasses a lack of transparenc.

The glass of my invention is relative y opaque, that is to say, translucent, while the heat resisting boro-silicate glasses, J as heretofore made, have been transparent or nearly so. Moreover, the glass in accordance with my invention has this advantage over other heat resisting glasses, that it can be more conveniently and cheaply produced; thebatch is melted at a lower tem-' perature; the control of the manufacture simplified and facilitated because less care and accuracy in the meltin operation is required; the glass produced is softer and more easily worked- I My invention, therefore, has for its objects, first, the production of a stable, heat resisting,- boro-silicate glass of novel character and properties; and, second, a new ai d improved method of producing such g ass. I

1 In carrying out my invention a batch is.

made up comprising, preferably, sand, boric acid, cryolite, and substances containing aluminum, sodium and potassium, and also magnesium and calcium. To the batch are preferably added, also, substances containing lithium, rubidium and caesium. While it is not essential to use all of the ingredients named there is an advantage in having ,oxide,10% to 20%, alumina 2% to 10%, alkali oxides (of sodium, potassium, lithium, rubidium and caesium) 5% to 10%, and oxides of the second group of the periodic system (magnesium and calcium) 0.5% to 2%.

the batch as complex as indicated. The

' As a specific example the following isba Glass 'made from this batch will have a chemical composition substantially as follows:

' Percent. Silica 74.38 Boric oxide 14.70 4 Sodium oxi 5.96 Aluminum oxide 3.45 Calcium oxide .22 Magnesium oxide .72 Potassium oxide .45

Lithium, rubidium and caesium oxides: .12

The batch is heated to a suitable melting temperature, for example, 2600 to 2800 Fahrenheit. The melt will be turbid, due to the colloidal condition of the alumina and possibl some of the other in edients. The silica, ric oxide and alk i oxides probably form' a true solution. The cryolite (Na,AlF,) breaks up forming, with oxygen,

'um oxide and aluminum oxide, the fluorine bein least. e sodium oxide goes into solution but the aluminum oxide will remain in a sus dad or colloidal state for a time.

Pro ably anv aluminum fluoride is 'formed which breaks down eventuall but leaves the alumina in such condition t at it does not immediately. dissolve. I understand that c'ryolite has been used as a flux in the manufacture of bore-silicate glasses but so far as I am aware it has not been employed for producing a colloidal condition in the melt preventing the complete solution of the a umina.

As soon as the ingredients have been'melted, and while the material is still turbid, preferably before planing has ceased, the application of heat to the batch is discontinued so as to preserve in the glass the colloidal condition produced in the melt.v The glass will be translucent in appearance and will be considerably tougher than the ordinary heat resisting glass of the boro-silicate type. Subjected to a deflection test, the fracture of the glass does not occur until some time after the glass begins to yield under a constant load. When ordinary glass is subject to a deflection test and the result plotted the breaking ints occurs in' the curve, almost immediate y after the yield point, that is, the point at which the glass begins to yield volatilized in a great measure atwithout additional load, the yield up tothie point having been substantially roportional to the increase in load. 1th the .millimeters per centigrade degree, between 20 centrigrade and 300 centigrade.

Tensile strength 9 kilograms per square millimeter. I

Youngs modulus of elasticity by deflection 6200 kilograms per square mlllimeter.

Density 2.29. Stability .0015 grams per centimeters. 4

Thermal endurance calculated by Winkelmann & Schotts equation '(Hovestadt, Jena Glass, MacMillan 1902, p. 229), 7.5. It may be said that the turbid or colloidal condition of the glass whereby the increased toughness is obtained, is dependent upon three factors: (1) the character of the batch,

it being essential that the batch contain an ingredient which will remain for a time in colloidal sus nsion, that is to say, not completely disso ved; (2) a melting temperature which is not too high, .too high a tem ture bringing about the dissolving o the suspended materialand (3) the duration of the heating perio it bem necessary to stop the a phcation of heat. fore the melt becomes 0 ear, thatis, before all the ingredients are completely dissolved. There is an interrelation betweenthese three factors. It is necessary, practically, to use ingredhundred square ients which will melt easily and at a relatively low temperature and which, when melted, will produce a turbid condition that will last foran appreciable time. If the turbidity disappears quickly, that is, if the ingredients all go into so tion very soonafter melting, it ma be possible to preserve in'the glass the co oidal condition of the melt but the necessity of calculating the temperatures and the length of the melting period, so that the melt will not become clear, would, under such circumstances, be so great as to make the operation impractical. With. the manufacture of the glass carried on as above described, the melt will remain turbid lon enough so that the pro er character of g ass can be obtained wit out inconvenience or excessive watchfulness.

I claim:

1. A. heat resisting glass containing silica, boric oxide, an alkah oxide and aluminum oxide, the latter being in colloidal condition.

2. A heat resisting glass containing silica 65% to 80%, by weight, boric oxide 10% to 20%, alkali oxides 5% to 10% and alumi- Ill num oxide 2% to the latter being in a colloidal condition.

3. Method of manufacturing a heat resisting glass of the boro-silicate type, which consists in producing in the melt a colloidal suspension of certain ingredients of the glass, and arresting the heating operation so as to preserve said colloidal condition in the product. I

4. Method of manufacturing a heat resisting glass of the boro-silicate type, which consists in meltin a batch containing silica, a boron compoun an alkali metal alumina, and a flourine com ound to produce a colloidal solution, an arresting the heating operation so as to preserve the colloidal condition in the product.

5. Method of manufacturing a heat resisting glass of the boro-silicate type, which consists in melting a batch containing silica, a boron compound, an alkali metal alumina and a flourine compound, and arresting the heating operation while the melt is still turbid to produce a translucent lass.

6. Method of manufacturing a eat resisting glass of the boro-silicate type, which consists in melting a batch containing silica, boric acid, an alkali metal, alumina and cryolite, and stopping the application of heat while the'melt is still turbid a translucent glass.

7. Method of manufacturing a heat resisting glass of the boro-silicate type, which consists in melting a batch containin silica, a boron compound, an alkali metal, a umina, an oxide of the second group of the periodic system, and a flourine compound to produce a colloidal solution, and arresting the heating operation so as to preserve the colloidal condition in the product.

8. Method of manufacturing a heat resisting glass of the boro-silicate type, which conslsts in melting a batch containing silica, a boron compoun-d, an alkali metal, alumina, an oxide of the second group of the periodic system, and a flourine compound, and arresting the heating operation while the melt is still turbid to produce a translucent glass.

9. Method of manufacturing a heat resisting glass of the boro-silicate type, which to produce consists in melting a batch containing silica,

boric acid, an alkali metal, an oxide of the second group of the periodic system, alum ina and cryolite, and stopping the operation of heat while the melt is still turbid to produce a translucent glass.

RALPH 1 BRENNER. 

